Abstract
Rapid and accurate estimations of the heterotrophic and autotrophic components of total soil respiration (Rs) are important for calculating forest carbon budgets and for understanding carbon dynamics associated with natural and management-related disturbances. The objective of this study was to use deep (60 cm) root exclusion tubes and paired control (i.e., no root exclusion) collars to estimate heterotrophic respiration (Rh) and Rs, respectively, in three 26-year-old longleaf pine (Pinus palustris Mill.) stands in western Georgia. Root biomass was measured in root exclusion tubes and control collars after 102–104 days of incubation and fine root biomass loss from root exclusion was used to quantify root decay. Mean Rs from control collars was 3.3 micromol·CO2·m−2·s−1. Root exclusion tubes decreased Rs, providing an estimate of Rh. Mean Rh was 2.7 micromol·CO2·m−2·s−1 when uncorrected by pretreatment variation, root decay, or soil moisture compared to 2.1 micromol·CO2·m−2·s−1 when Rh was corrected for root decay. The corresponding ratio of Rh to Rs ranged from 66% to 82%, depending on the estimation method. This study provides an estimate of Rh in longleaf pine forests, and demonstrates the potential for deep root exclusion tubes to provide relatively rapid assessments (i.e., ~40 days post-treatment) of Rh in similar forests. The range in Rh to Rs is comparable to other reports for similar temperate coniferous ecosystems.
Highlights
Anthropogenic emission of greenhouse gasses and concomitant global climate changes have fostered an impetus for the modeling and quantifying of global carbon stocks and balances within terrestrial ecosystems
Mean Rh was 2.7 micromol CO2 ̈ m2 ̈ s1 when uncorrected by pretreatment variation, root decay, or soil moisture compared to 2.1 micromol CO2 ̈ m2 ̈ s1 when Rh was corrected for root decay
We suggest that the longer incubation did not profoundly change soil moisture dynamics or our overall estimate of Rh to Rs, because soils in this study were sandy with excessive drainage and the presence of the root exclusion tubes increased soil moisture on the final measurement date by only about 1%
Summary
Anthropogenic emission of greenhouse gasses and concomitant global climate changes have fostered an impetus for the modeling and quantifying of global carbon stocks and balances within terrestrial ecosystems. Carbon sources for Rh from free-living soil microbes include soil organic matter, dead plant matter, and exudates from roots and Rh occurs in both root-free bulk soil and the root-affected rhizosphere [3]. In some woody species, including pines, CO2 is released by the metabolism of root exudates by ectomycorrhizal symbionts [4,5]. Sourced CO2 is a component of Rh , because of the interaction between roots and microbes in the Forests 2016, 7, 39; doi:10.3390/f7020039 www.mdpi.com/journal/forests
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